During periods of suckling continuous afferent input from peripheral mammary receptors of a variety of sensory modalities is transmitted to the central nervous system. Nevertheless, activation of oxytocinergic neurons, secretion of oxytocin and consequent milk ejection occurs in episodic bursts rather than in continuous fashion. Previous work suggests the existence of neuronal gating mechanisms that modulate and/or regulate afferent neural activity of the milk ejection reflex and thus determine the pattern of oxytocin secretion. In the present proposal neural gating mechanisms will be studied at several levels within the central nervous system and at the level of peripheral receptors in order to aid in the resolution of the questions (1) whether and (2) to what extent afferent neural activity determines the manner of activation of oxytocinergic neurosecretory neurons so as to account for their episodic activation and oxytocin secretory pattern. This will include (a) examination of the discharge pattern of oxytocin secreting neurons in relation to stimuli applied to central nervous sites and their interaction with simultaneous peripheral mammary receptor input, (b) examination of the central neuronal discharge pattern during transmission of mammary receptor input via spinal afferent fibers, and (c) examination of the discharge patterns from mammary receptors of different sensory modalities. This approach is expected to aid in the understanding of the milk ejection reflex by providing clearer definitions of sites and mechanisms of interaction of central nervous regulatory systems. In a broader sense it is expected that this study will form a basis for further investigation of other neuroendocrine regulatory systems. This work will further an understanding of the mechanism of brain-endocrine interaction in the neural regulation of the capacity of the female to secrete milk.